The collection of dirt and other particulates in an auto coolant system may be traced to many sources. One of the conventional sources is rust, which may form on cast iron heads and other cast iron auto components. The rusted metal surfaces of such components may become scaled with rust and rusted flakes may break off and flow into and with the coolant.
Other typical sources of particulate matter include transmission fluid, oil and exhaust gases. Combustion gases may contribute significantly to the collection of dirt and sludge in the auto coolant system.
Aluminum is a more recent source of particulate matter with the introduction of lightweight, aluminum auto components such as engine blocks. Unfortunately, aluminum corrodes. Whether the aluminum auto component is a water pump or engine head, small pieces of aluminum may tear from or break off the aluminum surfaces of the components. Such a cavitation corrosion may become especially severe on hot aluminum heads, where shock waves facilitate the corrosion. The shock waves are caused when coolant boils intensely around the hot aluminum exhaust ports and the boiling bubbles collapse. The collapsing bubbles create the shock waves, which increase the aluminum corrosion. After the aluminum chips tear from the aluminum auto components, they flow into and with the coolant to damage other engine parts or may even return to damage the very component off of which they were torn.
Another source of particulate matter is solder. Solder may corrode by reacting with coolant or antifreeze with chemicals such as glycol and silicone, and create "solder bloom" particles.
Another type of particulate is created by an electrolysis like reaction between the coolant and the liners of the engine block. One product of the electrolysis reaction is a water salt or white calcium like deposit which may precipitate out of the coolant to be carried with the coolant flow to plug up or damage other automobile components.
Still another source of particulate matter is sand. After an engine block is sand casted, auto manufacturers often fail to remove all of the sand from the block. The sand which remains is picked up by coolant.
Aluminum chips, calcium and solder bloom particles, sand, rust, dirt and sludge and other particulate matter flowing in coolant may damage a great variety of auto components. For instance, such particulates may flow into and plug the tubes of the radiator or heater core. Furthermore, the particulates, especially the aluminum chips, may slowly eat holes from the water jacket into the combustion chamber.
Free flowing aluminum chips and other particulates may also impair other engine components such as the coolant temperature sensor. In computer-controlled engines, the sensor triggers a computer program that monitors fuel mixture, timing and idle speed, among other functions. The sensor typically includes probes or exposed leads extending into the coolant flow to sense the coolant temperature. Particulates flowing at high speed may damage or destroy the probes which may ultimately result in poor fuel economy and a less responsive engine.
Moreover, many cars include at least one more coolant sensor for controlling the spin of the coolant fan, which is typically slowed down at highway speeds when air flow through the radiator is adequate for cooling. The coolant fan sensors are typically disposed in the bottoms of radiators and are rendered inoperable by flowing aluminum chips or the buildup of dirt, sludge, rust and other deposits.
To remove particulate matter, it is standard practice to flush the entire auto coolant system. The system is typically completely drained, and new antifreeze and water are added. With older cars having cast iron components, a flush every two to three years is advised. With more modern cars having aluminum components, flushing is typically an annual event.
One of the ways to flush out a coolant system is to install a flushing T in the heater-inlet hose and connect a garden hose to the T. A disadvantage with such a technique is that the rate of water flow and the water pressure in a garden hose may be undesirably high and cause damage to automobile components such as the heater core.